1. Field of the Invention
The present invention relates generally to a rearview mirror assembly for use in a motor vehicle and, more particularly, to a wake-up circuit for a remotely located vehicle control module embedded in a center-mounted rearview mirror assembly.
2. Discussion
Rearview mirrors, both center-mounted inside a vehicle passenger compartment and side-mounted outside the passenger compartment, are used to enable a driver of the vehicle to observe objects that are behind the vehicle while the driver's gaze remains directed generally forward. Such mirrors are ubiquitous means for providing actual visual images of objects that are behind the vehicles.
A significant amount of data is also presented to a driver of the vehicle in analog form (e.g., by gages) and/or in digital form (e.g., by digital display instrumentation). As recognized by the present invention, it can be advantageous to combine data sources not only to realize manufacturing cost savings, but also to promote safety and effectiveness in data presentation. In the context of a rearview mirror, the present invention recognizes that most drivers readily accept and use mirrors to know what objects are behind their vehicles, thereby improving driving safety. The present invention further recognizes that the use of mirrors can be promoted even further by presenting additional data on the mirrors to stimulate relatively more frequent use of the mirrors. Moreover, the effectiveness of the presentation of the data is improved by presenting data on a mirror that otherwise would be presented at a perhaps less convenient location in the vehicle. In other words, the present invention recognizes that it is possible that data presented on a mirror is more accessible than data presented in other locations that would not otherwise attract the driver's attention.
Nevertheless, problems exist with locating display devices on rearview mirror assemblies which may otherwise be exposed to considerable ambient light, such as in a convertible top vehicle. Therefore, it is also desirable to provide a display device for use in a mirror assembly, such as a liquid crystal display device, which does not exhibit diminished contrast when exposed to considerable ambient light.
It is further known to incorporate electronic components into the housing of a vehicle mirror assembly. For instance, it is known to mount courtesy lights and associated switches in the casing of an interior mirror assembly. In addition, electrochromatic rearview mirrors typically incorporate light sensors in order to detect light levels in the vicinity of the vehicle. In each of these cases, the electronic components are stand alone components which operate independent from the remainder of the vehicle data communication system.
On the contrary, a trip computer needs additional information from extraneous vehicle control modules in order to determine vehicle trip information. Most trip computers are located in the overhead console or in the instrument panel of the vehicle, and thus can be easily interfaced to the vehicle data communication system. However, in some convertible top vehicles there is no room to package a trip computer in the instrument panel of the vehicle.
Therefore, it is desirable to provide a rearview mirror assembly which incorporates a trip computer. In order to receive extraneous vehicle trip information, additional wires would have to be run from the trip computer in the mirror assembly to the instrument panel or other electronic components. As a result, the manufacturer would likely incur substantial additional costs for incorporating a trip computer into the mirror assembly. Thus, it is also desirable to interconnect the trip computer embedded in the mirror assembly via a single wire bus network to the other vehicle control modules in the vehicle. In this way, the trip computer no longer needs to be hardwired to receive an ignition on signal which is used to power up the mirror assembly. Moreover, the trip computer has access to any additional information needed for determining and displaying vehicle trip information. Lastly, it is desirable to provide a wake-up circuit which upon detection of bus activity over the bus network is able to power up the trip computer.